283     /**
 284      * Returns the current subject.
 285      *
 286      * <p> The current subject is installed by the {@link #callAs} method.
 287      * When {@code callAs(subject, action)} is called, {@code action} is
 288      * executed with {@code subject} as its current subject which can be
 289      * retrieved by this method. After {@code action} is finished, the current
 290      * subject is reset to its previous value. The current
 291      * subject is {@code null} before the first call of {@code callAs()}.
 292      *
 293      * <p> This method returns the
 294      * {@code Subject} bound to the period of the execution of the current
 295      * thread.
 296      *
 297      * @return the current subject, or {@code null} if a current subject is
 298      *      not installed or the current subject is set to {@code null}.
 299      * @see #callAs(Subject, Callable)
 300      * @since 18
 301      */
 302     public static Subject current() {
 303         return SCOPED_SUBJECT.orElse(null);
 304     }
 305 
 306     /**
 307      * Executes a {@code Callable} with {@code subject} as the
 308      * current subject.
 309      *
 310      * <p> This method launches {@code action} and binds {@code subject} to the
 311      * period of its execution.
 312      *
 313      * @param subject the {@code Subject} that the specified {@code action}
 314      *               will run as.  This parameter may be {@code null}.
 315      * @param action the code to be run with {@code subject} as its current
 316      *               subject. Must not be {@code null}.
 317      * @param <T> the type of value returned by the {@code call} method
 318      *            of {@code action}
 319      * @return the value returned by the {@code call} method of {@code action}
 320      * @throws NullPointerException if {@code action} is {@code null}
 321      * @throws CompletionException if {@code action.call()} throws an exception.
 322      *      The cause of the {@code CompletionException} is set to the exception
 323      *      thrown by {@code action.call()}.

 283     /**
 284      * Returns the current subject.
 285      *
 286      * <p> The current subject is installed by the {@link #callAs} method.
 287      * When {@code callAs(subject, action)} is called, {@code action} is
 288      * executed with {@code subject} as its current subject which can be
 289      * retrieved by this method. After {@code action} is finished, the current
 290      * subject is reset to its previous value. The current
 291      * subject is {@code null} before the first call of {@code callAs()}.
 292      *
 293      * <p> This method returns the
 294      * {@code Subject} bound to the period of the execution of the current
 295      * thread.
 296      *
 297      * @return the current subject, or {@code null} if a current subject is
 298      *      not installed or the current subject is set to {@code null}.
 299      * @see #callAs(Subject, Callable)
 300      * @since 18
 301      */
 302     public static Subject current() {
 303         return SCOPED_SUBJECT.isBound() ? SCOPED_SUBJECT.get() : null;
 304     }
 305 
 306     /**
 307      * Executes a {@code Callable} with {@code subject} as the
 308      * current subject.
 309      *
 310      * <p> This method launches {@code action} and binds {@code subject} to the
 311      * period of its execution.
 312      *
 313      * @param subject the {@code Subject} that the specified {@code action}
 314      *               will run as.  This parameter may be {@code null}.
 315      * @param action the code to be run with {@code subject} as its current
 316      *               subject. Must not be {@code null}.
 317      * @param <T> the type of value returned by the {@code call} method
 318      *            of {@code action}
 319      * @return the value returned by the {@code call} method of {@code action}
 320      * @throws NullPointerException if {@code action} is {@code null}
 321      * @throws CompletionException if {@code action.call()} throws an exception.
 322      *      The cause of the {@code CompletionException} is set to the exception
 323      *      thrown by {@code action.call()}.